First you need to define your requirements.

1. Is just for browsing and the router will be connected to a VDSL link with something like 100/250mbit?
2. Are you planning to have a server at home and transfer a lot of data within your LAN and need a lot of throughput?

If it's 1, then you can get a bunch of used ac routers, something like Archer C5 or C7, flash OpenWRT on it and configure 802.11r within your LAN. This requires some fiddling, but you don't need to spend a lot of money on a decent mesh.

For 2, well you with with €200 budget it's going to be trikcy.

check out OPNsense routers and use your existing equipment only as access points. You can then make firewall rules to block them from phoning home. protectli sells some inexpensive models.

It is probably Chinese junk, but I'm using a set of cudy m3000 WiFi6 mesh devices that run openwrt. Could be worth looking into. They are about as cheap as I've seen. There should be WiFi7 versions out nowish /soon.

Does it have to be new? I can consistently find used ac lites from unifi on Kleinanzeigen.de for 50€, I got two of those and later a 6 lite for another 50€, that's half my network. They are old and out of warranty, but use very low power and have really decent speeds (~500mbps).

It might be helpful to specify your network needs. The system you linked is a WiFi 5 system. That's 10+ year old technology.

What kind of speeds are you looking for? Will your access points be wired or wireless?

You can just setup an extender where you need it. That is what I have. No real need for mesh unless your place is really big.

I ditched Netgear due to poor performance and went with Ubiquiti. I'm fortunate that I could afford to buy a console for management but if you're willing to self-host then there is no cost there. You could then get several APs (they have some as low as $99) and you're all set.

If you can handle steep learning curve with less proven stability, Mikrotik.

Maybe https://www.gl-inet.com/

As I understand their stuff runs a custom OpenWRT, so you can use them as-is, or if you want vanilla OpenWRT it's very easy to flash them.

As far as Mesh goes I'm not sure how they would do, for mesh to perform well you need a system that has dedicated mesh radios in the 5/6ghz bands, and only the more expensive mesh systems typically have that.

Do you have requirements for the WiFi Standard?

Do you want to build up a new system or adding to your current setup?

For the price point you could look into the AVM Fritz Ecosystem. Their Mesh solution is quite hassle free and for 200€ you could get WiFi 5 capable devices on the used market.

Not sure how well they work with other brands, so you might want to invest in a FritzBox and FritzRepeater (should be in the budget used).

Anything above WiFi 5 could be out of your price range, especially new.

Ubiquity APs with WiFi 5 could be in your budget, even new. Look into the AP HD. You will need a controller installation though, weither on your desktop or on a NAS, Server. You do NOT need to buy an appliance from them for management. They do not make it clear on their website.

If you are willing to do your homework:
https://openwrt.org/docs/guide-user/network/wifi/mesh/start

I'm also looking for a good WiFi mesh, preferably one that can be used with IoT devices (aka. Even without an internet connection).

I tried TP-Link Deca, but the mesh refuses LAN communication if the router doesn't have a constant and stable connection to the internet - A feature I previously believed to be given - making it unusable for IoT and for providing WiFi at remote locations.